موسوعة كتب ـ الأصول الأربعة عند الشيعة is an iPhone application that includes the four books known as the Four Principles among Shia Muslims. These books are Al-Kafi, Tahdhib al-Ahkam, Al-Istibsar, and Man La Yahduruhu al-Faqih, complete with all their parts.

One of the key features of this application is that the books included are an accurate representation of the original texts in terms of page numbers. Users can also access a complete index for each book and search for specific words or phrases across all the books or within a single book independently.

The application provides a comfortable reading experience by allowing users to customize the font size and type, adjust line spacing and brightness, and choose a night mode for easier reading. The user-friendly interface makes it easy to navigate through the books and access the desired content quickly.

Overall, موسوعة كتب ـ الأصول الأربعة عند الشيعة is a valuable resource for Shia Muslims looking to study and explore the Four Principles in a convenient and accessible way on their iPhones.